A principle goal of modern medicine has been the reduction of trauma associated with various surgical procedures. When surgical invasiveness and trauma are reduced the associated surgical complications are correspondingly reduced. As a result, the less invasive the surgical procedure the greater the chances for a rapid, uncomplicated recovery. A recent successful development in the field of less invasive surgery is the medical procedure known as angioplasty. Angioplasty has become a widely accepted method for opening obstructions or stenoses throughout the vascular system, particularly in the coronary arteries.
The most common form of angioplasty practiced to date is known as percutaneous transluminal coronary angioplasty (PTCA). In virtually all forms of this procedure a dilatation catheter having an inflatable balloon at its distal end is guided through the patient's artery and the balloon is positioned across the stenosis. Once in place the balloon is inflated for a brief period of time in order to displace or deform the occluding lesion. After the stenosis has been opened and adequate blood flow has been reestablished the catheter is withdrawn. In this manner, it is possible to open blocked coronary arteries through a small vascular incision without the serious risks and complications previously associated with open heart surgery.
In most forms of angioplasty the dilatation catheter is guided into position through the patient's arteries utilizing a very small diameter flexible guidewire. Typically, guidewires are formed of surgical grade stainless steel having a diameter on the order of 0.010 to 0.015 inches and an overall length of approximately 175 cm. The distal end of the guidewire is extremely flexible and may be formed as a coil of very small diameter wire to enable the cardiac physician to direct the guidewire along the branched and convoluted arterial pathway as the guidewire is advanced to the target site. Once the guidewire is positioned across the lesion an appropriately sized dilatation catheter is advanced "over-the-wire". At this point in the procedure the dilatation balloon is in a deflated configuration having a minimal cross-sectional diameter which facilitates its positioning across the lesion prior to inflation. At various times throughout the procedure radiopaque dyes are injected into the artery to enable the cardiac physician to visualize the catheter and target vascular pathway on a fluoroscope.
An undesirable complication associated with the utilization of such "over-the-wire" dilatation catheters is the need to extend the guidewire outside of the patient's body a sufficient distance to enable the over-the-wire catheter to be threaded onto the guidewire without disturbing the positioning of the guidewire across the target lesion. Typically, a guidewire extension is "docked" or affixed to the proximal end of the guidewire in order to provide the additional length necessary to thread the guidewire into the catheter. As the typical dilatation catheter ranges in length from 120 cm to 160 cm the guidewire extension can be quite long and awkward to manipulate as it extends outside the patient's body. Alternatively, an exceptionally long guidewire on the order of 300 cm in length may be positioned initially and subsequently exchanged with a shorter, easier to handle guidewire after positioning of the catheter. In either case, an additional medical assistant may be necessary solely to monitor or manipulate the guidewire or its extension. Moreover, the junction between the docked guidewire end and the docked extension may interfere with the smooth advancement of the catheter along the guidewire decreasing the physician's control of the procedure.
A number of alternative dilatation catheter designs have been developed in an attempt to reduce or eliminate these problems. For example, "fixed-wire" dilatation catheters incorporating an internally fixed guidewire or stiffening element have been utilized with some degree of success. In addition to eliminating the need for guidewire extensions, these fixed-wire designs are smaller in diameter than their over-the-wire counterparts because the balloon inflation lumen is also utilized to contain the fixed guidewire. As a result, these designs are quite maneuverable and relatively easy to position. However, the most significant drawback associated with fixed-wire catheter designs is the inability to retain guidewire access to the target site while removing the catheter. Removal or replacement of a balloon catheter is not an uncommon occurrence during balloon angioplasty. Should it become necessary to perform such a removal or exchange procedure the fixed guidewire also must be removed simultaneously. This greatly complicates reaccessing the lesion with a subsequent device if desired.
Similarly, an additional drawback of fixed-wire catheter designs is the inability to exchange the guidewire. Though relatively rare, replacement of a guidewire is sometimes required when the original wire is broken or defective, or when the wire tip must be reshaped to perform the procedure. With these fixed wire unitary designs the entire assembly must be removed forcing the vascular physician to renegotiate the arterial pathway with a new catheter and guidewire combination.
An alternative catheter design is the "monorail" variant of the over-the-wire system such as that disclosed in U.S. Pat. No. 4,762,129 issued Aug. 9, 1988 to Bonzel. This catheter design utilizes a conventional inflation lumen plus a relatively short parallel guiding or through lumen located at its distal end and passing through the dilatation balloon. This design enables the short externally accessible monorail or guidewire lumen to be threaded over the proximal end of a pre-positioned guidewire without the need for docking a guidewire extension. Additionally, because the guidewire lumen is quite short the guidewire remains external to all portions of the catheter proximal to the distal portion of the catheter and frictional drag along the guidewire lumen reportedly is reduced. Thus, it is possible to recross an acutely closed lesion or to exchange balloon catheters without losing guidewire access or docking an extension wire.
However, in spite of this success a significant disadvantage associated with monorail dilatation catheters is the difficulty in steering the catheter along the guidewire through tortuous or convoluted vascular pathways. Because the guidewire is not supported within the catheter it is possible to wrap the distal end of the catheter around the guidewire as vascular curves and junctions are traversed. Additionally, though it is possible to remove the guidewire and leave the monorail catheter in position, it is virtually impossible to replace or exchange the guidewire if necessary as it is impossible to reengage the distal monorail guidewire lumen once it is positioned in the patient's body.
A more recent attempt at dealing with these problems is disclosed in U.S. Pat. No. 4,988,356 issued Jan. 29, 1991 to Crittenden et al. This catheter and guidewire exchange system utilizes a connector fitting mounted on the proximal end o the catheter and a longitudinal slit formed in the catheter shaft and extending from the proximal end proximate the connector forward towards the distal end. A guide member mounted on the fitting directs the guidewire through the slit and into the guidewire lumen in response to relative movement of the guidewire or catheter. This system reportedly avoids the need for a long exchange wire as well as the problems of a monorail design yet it presents several drawbacks of its own. First, the additional exchange fitting adds complexity to the design and function of the catheter. Further, the added drag induced by the fitting as it spreads the slit during catheter movement reduces the feel and control of the catheter as it is advanced along the guidewire. Moreover, because the slit terminates at a position distally to the proximal end of the catheter it is not possible to completely remove the catheter from the guidewire in a simple procedure. Reengagement of the catheter on the guidewire is even more complex.
Accordingly, it is an object of the present invention to provide a dilatation balloon catheter design that can be fully exchanged easily without sacrificing guidewire access to a target lesion. A concurrent object of the present invention is to provide such a dilatation catheter that can traverse branched arteries and vascular curves and bends with the ease of an over-the-wire design.
It is a further object of the present invention to provide a dilatation catheter that facilities the exchange or replacement of a guidewire if necessary.
It is yet an additional object of the present invention to provide a dilatation catheter with all of the advantages and features of an over-the-wire design that also provides the ability to be removed from a pre-positioned guidewire rapidly and simply without utilizing a guidewire extension or long exchange wire.
It is an additional object of the present invention to provide a fully exchangeable over-the-wire balloon catheter which will allow for catheter exchange without the need for docking a guidewire extension or utilizing a long exchange wire.